They are actually a Triad! A split complementary Triad to be exact. This question actually made me think about the coloring of each member. I mean logically, If their name is 'aka' tsuki, and they primarily wear red, why wouldn't their leader be red? But when you put all of their colors on a color wheel, Keito's green looks a little like it's pulling the Purple and Red (warmer colors) together :). But even then, Keito's green is a little on the yellow side. All three of them have colors that go best with gold, which is scattered throughout their unit outfits. Another neat thing is that their image colors (while not exact) match very closely to a lot of traditional Japanese colors (Yes those are a thing). Kuro matches 'Pure Red', Keito matches various shades of 'Green Onion' and 'Willow', and Souma ranges from 'Wisteria' to 'Bellflower'.

Check it out! https://en.m.wikipedia.org/wiki/Traditional_colors_of_Japan